VITAL PHENOMENA OF PROTOPLASM. 175 



cells of a tissue with the nutritive material which they absorb. In all the higher 

 .animals this nutritive material is the blood or lymph, but the products which are 

 formed are not entirely the same for all cells, since they vary in some measure with 

 the specific activity of the cell ; thus the cells of the salivary glands yield the saliva, 

 those of the mammary gland milk, and those of the liver form, besides other substances, 

 glycogen. But all protoplasm, whatever may be its specific function, has this in 

 common, viz., that it absorbs and combines with oxygen, and yields carbon dioxide 

 and other products of oxidation, and as a result of these processes of oxidation heat 

 and other kinds of energy are produced. These chemical changes are always more 

 marked as the functional activity of the cell becomes increased, and accordingly any 

 circumstances which tend to promote the activity of protoplasm, such as warmth, 

 electrical or other stimulation, the action of certain drugs, tend proportionally to 

 increase the activity of its chemical processes. One general chemical property 

 of living protoplasm is that by virtue of which it is able to assimilate and eventually 

 to convert into its own substance non-living proteid material. In this manner the 

 protoplasm of a cell may increase in amount, or in other words the cell may grow ; 

 but if the amount of protoplasm does not permanently increase, this is due to the fact 

 that just as much protoplasm is being broken down and removed from the cell as is 

 added by the process of assimilation. Chemical processes which involve the building 

 up of living material within a cell have received the general name of anabolic changes ; 

 those on the other hand which involve the breaking down of such material into 

 other and simpler products are known as Tcatabolic. By the metabolism of a cell is 

 understood the sum of all the ana- and katabolic changes which are proceeding at 

 any time within it. 



Amoeboid movements. The most obvious physical changes seen in living 

 protoplasm are those which are designated "amoeboid." This term was derived 

 from the freshwater amoeba, the protoplasm or sarcode of which has long been known 

 to exhibit spontaneous changes of form, accompanied by a flowing or streaming of 

 its soft semifluid substance. The phenomenon was in fact described by Rosenhof in 

 1755, but the similar movements of the cell-protoplasm of the higher animals was 

 only recognised much later (in 1846 by Wharton Jones, who noticed the amoeboid 

 movements of the white blood-corpuscles of fish). If the protoplasm of the cell is 

 enclosed by a membrane its movements are necessarily confined within the limits of 

 such cell- wall, and the actual changes which are in these cases observable consist in 

 a streaming or flowing of the soft living substance, such flowing being rendered 

 obvious by the carrying along by the stream of any minute particles which may be 

 imbedded in the protoplasm. The term " rotation " has been given to a movement 

 of this kind which is observed in many plant-cells, and is of a very regular 

 character, and usually in a determinate direction ; but in animal cells the intrinsic 

 streaming movements are less regular and usually less obvious in character. It is, 

 however, on the other hand in those animal cells which are unprovided with a cell- 

 wall (free or naked cells) that what may be termed the amoeboid movements 

 proper present themselves, and in none more strikingly than in the pale blood- or 

 lymph-corpuscles. If one of these be observed under a high power of the microscope 

 it will be seen gradually to protrude a portion of its protoplasm at one part or 

 another, and sometimes at several places simultaneously. These protrusions (pseudo- 

 podia) may be presently withdrawn again and others given out, or a pseudopodium 

 which has been protruded at any one part of the corpuscle may extend itself further, 

 and the main part or body of the corpuscle may pass gradually towards and into the 

 extending pseudopodium. By a repetition of this process the cell may glide slowly, 

 away from its original situation, and move bodily along the field of the microscope 

 so that an actual locomotion thereby results. In this manner the white corpuscles 

 may, even while the blood is circulating, pass through the walls of the capillaries and 



